The present invention relates to the purification of phenol and particularly to the production of high purity phenol from technical or refined grade phenol which has been produced by the cleavage of cumene hydroperoxide.
A major source of phenol for many applications is the oxidation of cumene to cumene hydroperoxide and the acid cleavage of cumene hydroperoxide to a mixture of phenol and acetone which typically also contains unreacted cumene and side products such as alpha-methylstyrene, various carbonyl compounds and various benzofuran compounds. The mixture is generally subjected to a series of distillations to recover various fractions including a crude phenol fraction. Fractional distillation of the crude phenol fraction, under various conditions, produces a "technical", "refined" or water-white grade which is sufficiently pure for many purposes. Such phenol is unsatisfactory, however, for certain purposes and, in particular, when chlorinated or sulfonated with sulfuric acid, the phenol becomes red. Additionally, such phenol, itself initially gray, generally discolors on aging, becoming darker and eventually black. These effects may be due to either ketonic impurities such as mesityl oxide, acetol and acetophenone or to benzofuran impurities such as methylbenzofuran which may be formed by reaction of certain ketonic impurities such as acetol with phenol.
The purification of such technical refined grade phenol by chemical treatment is described, for example, in U.S. Pat. No. 3,692,845 to Cheema et al. (Sept. 19, 1972); U.K. Pat. No. 883,746 to National Distillers Company (Dec. 6, 1961); U.S. Pat. No. 2,864,869 to Crocker et al. (Dec. 16, 1958); U.K. Pat. No. 1,108,327 to Universal Oil Products Company (Apr. 3, 1968); U.K. Pat. No. 1,148,907 to Imperial Chemical Industries Limited (Apr. 16, 1969) and U.S. Pat. No. 2,971,893 to Hood (Feb. 14, 1961). The present invention is applicable to processes of purification which include treatment of the phenol with a base such as alkali metal hydroxides or carbonates or monoamines or diamines as described in U.K. Pat. No. 883,746 or hydrazines as described in U.S. Pat. No. 2,864,869 or alkaline hydrogen peroxide as described in U.S. Pat. No. 2,971,893. The present invention is especially applicable to processes of purification which include treatment with polyamines followed by the addition of acid or acid anhydride followed by distillation as described in U.S. Pat. No. 3,692,845. The present invention also includes steam and product distillations as separate steps, which are also described as separate steps in U.K. Pat. No. 883,746 and U.S. Pat. No. 2,971,893.
The object of the present invention is to achieve phenol of high purity from technical or refined grade phenol or from impure phenol streams with a minimal use of energy, and especially a minimal use of steam in the steam distillation. This is accomplished by careful control of the chemical treatment to minimize the formation of certain hard to separate impurities during the treatment and by extraction of the overheads of the steam distillation.